Amplifying circuits



Jan. 14, 1930.7 v. D. LANDON 1,743,143

AMPLIFYING CIRCUITS Filed April 12, 1926 WITNESSES: INVENTOR Verna/70; Landon AT'TORNEY Patented Jan. 14, 1930 PATEN VERNON D. LANDON, OF EAST PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO VTESTTNG- HOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- VANIA AMPLIFYING CIRCUIT$ Application filed. April 12 1926. Serial No. 101,286.

My invention relates to systems for the amplification of high-frequency varying currents and it has particular reference to such systems making use of the super-regenerative principle to greatly increase the amplification obtained.

In the patent to Armstrong, No. 1,424,615, there is disclosed and claimed a system of amplification wherein the signal strength obtainable is much greater than with the ordinary amplifying systems. The system disclosed by Armstrong makes use of the wellknown principle of regeneration but further embodies means for periodically stopping the regenerative action. Systems of this general type have come to be known as super-regenerative by reason of the fact that, with the same number of tubes, they give a greatly increased volume of output.

In operation, there is constantly generated in the super-regenerative system a local or variation frequency, which may reach a considerable amplitude. When the super-regenerative system is coupled to an antenna in the usual and well-known manner, this variation frequency is radiated and is extremely annoying to persons operating receiving sets in the near vicinity. It is also noted that with the super-regenerative system alone, the tuning is quite broad and considerable difficulty is experienced in separating the carrier waves of stations broadcasting on frequencies which difier but slightly from each other. For these reasons, the super-regenerative circuit has not gone into very extensive use.

It is, accordingly, one object of my invention to provide means whereby a super-regenerative system will be prevented from radiating.

Another object is to sharpen the tuning of a super-regenerative system.

Another object is to increase the sensitivity of a super-regenerative system.

Still another object is to so arrange a superregenerative system that is extremely easy to tune.

A further object is to so improve the Sta-- bility of a super-regenerative amplifying system that the reception of signals will not be interrupted by undesired oscillations.

I attain these objects, and others which will be stated later, by interposing between the antenna or source of signal energy and the super-regenerative system, an amplifier which is so arranged that signal energy may pass from the antenna to the super-regenerative system but cannot pass in the reverse di-- rection. y

More specifically, I employ, between the antenna and the super-regenerative detector, one or more steps of radio frequency amplification, each of which is'neut-ralized against oscillation according to the teachings of Rice Patent No. 1,33A,118. The interposition of one or a plurality of steps of neutralized radio frequency amplification between the source of varying energy and the super-regenerative amplifier prevents the local oscil lations of the amplifier from reaching the antenna, stabilizes the signal voltages impressed on the super-regenerative system and gives rise to additional unforeseen advantages which will be brought out later.

Referring now to the drawing and the fol lowing description, from which a more complete understanding of my invention may be had,

The single figure is a diagrammatic view of a preferred form of my invention, in which the radio frequency amplifier is shown as a single step.

An antenna 1 is connected through a variable condenser 2 and a variable inductor 3 to the ground 4:. This is merely indicative of a source of varying signal energy as my invention may be employed with other signal sources. Variably coupled to inductor 3 is a second inductor 4 shunted by avariable condenser 5, connected between the grid 6 and 'throughacondenser 13. The inductors 11..

and 12" are preferably formed as a single coil with a tap at, or near, the center for the connection from the battery 12. The output inductor-11 is coupled to an inductor 14,

which is-shunted byacondenserlti, the ele ments 14 and 15 being connected in the grid circuit of a second thermionic device-17l The thermionic device 17 is providedwith a grid 18, a filament 19 and an anode 20in the usual andWell-known manner.v The filament is provided" with a source of'power 22 and in series with the, anode, 20 and the filament 19 is a tickler. or. feerl-b'ack coil 23,.a pair of telephones24; a source of'an-ode potential 25, and-a tuned cirouit comprising inductor 26 and condenser 27; lncludedi serially between thetuned' circuit 1'4i15. and the filament 19 I is another tuned circuitcomprising inductor 28 and condenser 29; A grid biasing battery 31" may be used, if'desirable, and the telephones 24c'may be by-passedby a condenser 82.

In the operation of my system, the incoming signals, which are impressedby way of 3a inductor 4 across the gridfilament circuit of" the thermionic device 8, are amplified therein and are repeated with greatly increased amplitude in the output inductor 11. Tha -functionv of the inductor 12"andthe V 40 condenser-13h: to impress upon the grid'of the device 8 a potential 180 outof phase with any potentialimpressed upon the inductor.

11 by reason of its coupling with the inductor 14'. The capacity of the condenser '13 is so chosen'that the productof'thiscapacity and theinductance ofthe inductor 12'is equal to the productof the-capacity existing between the grid6 and "theanode .9, and-the inductor Hi .1 By reason of'thisconnection, varying-potentials induced: in inductor 11, on accountv of; current changes in inductor 14:, will not cause any potential tobe'setup in inductor; 4 since the condenser13 will apply to the grid- 7 a voltage"180"out of phasewith-the' voltage applied thereto through-- the grid anodecapacity; This system of neutralization is within the teachings of the Rice'patent referred to: The:signa-l; variations, however,

60,, existing in theoutput inductor 11' are impressedthroughthe coupling between inductors 11' and'ltrupon the input circuit of. the super-regenerative system, illustrated at the right of the dotted line.

As explainedinthe Armstrong patent referred to, inductors 28 and 26, together with condensers 29 and 27, control the rate at which high frequency oscillations in the super-re generative system are started and stopped. This variation frequency is usually in the neighborhood of 10,000 cycles per second and, if allowed to react on the antenna system 123-4, would prove extremely annoying to the operators of neighboring receiving sets. Such reaction is further detrimental by, reason of the fact thatlthe oscillations setup in the super-regenerative systemwould persist in the antenna circuit after the cessation of an incoming signal, and would act as atrigger to set'the super-regenerative system again into oscillation, causing the signal to become blurred. v

This feed-back of energy from the superregenerative system into the antenna gives rise to a broa'dness of tuning which, as explained above, ,is, undesirable. By, providing the thermionic amplifierdevice 8, which: is. interposed between. the antenna. and the super-regenerative system, with means. for. the prevention .offeed-back therethrough, all so oscillations in the super-regenerative portion. of the system are prevented from reaching the antenna.

. It is also feasible to use aloopinsteadioff the antenna shown,.and inisuchcase'lfmay, 95.- provide the loop with a center tap ,to thefilaw ment of thedevice 8, and with a connection through a condenser to the anode 9 from the; end attached to the grid.

It is noted,- whenoperating asystem ar- 4 rangedaccordingto my invention, that the. tuning is much sharper thanvus uali. It.is, also notedthat the sensitivity of the systemas whole is greatly'increased, permittingthe re.- ception of signals, from, stations ordinarily out ofreachof. the usual super-regenerative circuit.

lVhen {properly adjusted, the system of my invention will cause no annoyance to persons operating other receiving sets-near by. His 11o extremely stable in operation anddisplays no tendency to produce undesired oscillations.

Although I. have illustrated ands described hereina specific embodiment of my invention,

I" am fully aware that many other 'modifica- 1 tions are possible. I, accordingly, denotintend to be limited except in so faras is necessitated by prior art'and is indicated in the scope of the appended claim.

I claim :as my invention? I 129 In a signalTreceiving-system, athermionici amplifier having input: and output: terminals, means, capable of. oscillating," for. receiving: signal energy and-impressing, it; across said input terminals, a super-regenerative detector capable of simultaneously generating oscillations at a plurality of frequencies,.cou-- pling means between the output terminals of said amplifier and said detector for transferring signal energy to. said detector, and an 130 auxiliary coil and condenser connected between the input terminals of said amplifier and being so inductively associated with the aforesaid coupling means as to apply potentials across said amplifier input terminals out of phase with the oscillatory potentials applied thereacross from the detector by reason of the inter-electrode capacity of said amplifier, whereby the signal-energy-receiving means is prevented from being kept in a state of oscillation by energy from said detector, and the sharpness of tuning of the system is increased.

In testimony whereof, I have hereunto subscribed my name this 29th day of March, 1926.

VERNON D. LANDON. 

